So I have march underdrive pulleys installed in my car, a optimus yellowtop battery and a Powermaster 140 amp alternator. All pretty new. Ever since I put these on I've had charging issues. Sympotms used to be slightly dim headlights at low rpm and an initial slight bogy feeling when I hit the gas I think mabye because of poor spark. Anyway now my battery won't charge after jump starts. I jump the car run it 100 miles and it will barely start again if at all. I think my alternator/underdrive pulleys are just not working well together. The summit racing tech guy said its a common problem. Is it? Obviously I need to test the alternator to make sure its pumping out at around 14 but I'm wondering if there is a solution to this or what you guys think. sorry so long. thanks.

 

With underdrive pulleys, you are spinning the accessories slower - including the alternator, so its putting out less power, especially at low speeds. And don't use the alt to charge the battery, its only to maintain a fullish charge. Charge it with a battery charger, or you will overwork the alternator and burn it out.

 

Any suggestions on my crappy setup? Seem like a great idea on paper...

 

yes get a smaller alternator pulley. SUmmit sells one by march. Power and Amp series designed for underdrive setups

thats the setup i have, with a smaller alternator pulley and i have NO issues at all. Even with battery in the trunk.


Do you have V belts or serpetine belt?

this for serpetine belts should do it
http://store.summitracing.com/partde...5&autoview=sku

V belts i'm not sure, but make sure its SMALLER diameter than the one you are using

 

Basically your only option is to get the alternator spinning at the correct speed, so that it can make enough power to keep the battery topped up. Only way to do that is:

A) Go back to the original pulley setup, which was either a larger crank pulley, smaller alt pulley, or both, to get the alternator RPM to go up to where it needs to be. You can also just get a smaller alt pulley than what you have, March probably makes one.

B) increase engine speed - don't go this route.

You'll probably notice too, with the underdrive setup, that the engine will run warmer too at low speeds, because the waterpump is also not turning as fast as it was. My suggestion - install the regular size pullies, and sell the underdrive stuff to someone who wants its for a mostly-track car. The very small benefits of underdrive pullies do not outweigh the PITA factor of... well, problems like you are having. Just my .02

 

I agree with you 100% Adam on the small benefits and the pain in the a$$ reality. However I no longer have my original pulleys and don't really want to spend the time changing it over again and I love the look too since I'm working on a potential showcar.
Thanks for the tip RocZ on the alternator pulley. Ya that one is a little smaller than mine I think I'll order one. Seems like it couldn't hurt. My setup is serpentine.

 

it will work. I ran underdrive crank pulley on stock alternator pulley and had same dim lights at night...voltage drops and hard starts. Swapped the pulley and its fine now

 

Just do like Orr said, and get the smaller alternator pulley from March, then your charging problem should go away, or at least improve. They should make one that has a visual match to the set you bought, just in a smaller diameter I would think?